iOS － self & super 理解的关键点

1. method 搜寻路径

（在运行时，调用的到底是哪个 setOrigin::）

- reposition
{
 ...
 [self setOrigin:someX :someY];
 ...
}

或者：

- reposition
{
 ...
 [super setOrigin:someX :someY];
 ...
}

规则：

系统在解析 self 的时候，跟继承链没关系，哪个对象收到消息，self就指的是哪个对象，也就是运行时确定 self 到底指的是谁；
系统在解析 super 的时候，似乎是编译时就定死了，就看 super 是在哪个类方法里出现的，然后调用其父类（或者沿着继承链向上追溯）的该方法，跟消息的接收者没关系。


2. self 在不同语境下有不同含义：

Inside an instance method, self refers to the instance; but inside a class method, self refers to the class object. 

This is an example of what not to do:

+ (Rectangle *)rectangleOfColor:(NSColor *) color
{
 self = [[Rectangle alloc] init]; // BAD
 [self setColor:color];
 return [self autorelease];
}

To avoid confusion, it’s usually better to use a variable other than self to refer to an instance inside a class

method:

+ (id)rectangleOfColor:(NSColor *)color
{
 id newInstance = [[Rectangle alloc] init]; // GOOD
 [newInstance setColor:color];
 return [newInstance autorelease];
}

In fact, rather than sending the alloc message to the class in a class method, it’s often better to send alloc
to self. This way, if the class is subclassed, and the rectangleOfColor: message is received by a subclass,
the instance returned is the same type as the subclass(for example, the array method of NSArray is inherited

by NSMutableArray).

+ (id)rectangleOfColor:(NSColor *)color
{
 id newInstance = [[self alloc] init]; // EXCELLENT
 [newInstance setColor:color];
 return [newInstance autorelease];
}

这些是从apple官方文档里摘录的，英文很简单，再配合例子，就没必要翻译了。